Generally speaking, energy saving light sources, such as compact fluorescent lamps (CFLs) and light emitting diode (LED) lamps, have become more popular in recent years. With these light sources, however, more working areas are subjected to ambient light having high frequency flickering. Laser-based barcode scanners can experience difficulty functioning properly as a result of such flickering light interference.
The flicker from ambient lights in the vicinity of laser-based barcode scanners can introduce noise or interference into the scanned optical signals of the barcode scanners. For instance, fluorescent lights have high-frequency electronic ballasts and light emitting diode (LED) lamps have high-frequency drivers. These high-frequency components generate pulsed illumination on barcode symbols. This pulsed illumination can be received by the barcode scanner as optical noise. The noise can introduce false edge detection, which can result in difficult or incorrect decoding of the barcode by the barcode scanning circuitry.
FIGS. 1A and 1B are graphs derived from screen shots obtained during a signal analysis test to determine the noise from ambient lights and the subsequent interference to the proper scanning processes of laser-based barcode scanning devices. Graph 10 of FIG. 1A shows signals received from a first barcode scanning process. In the first process, the barcode scan signals were obtained when a particular ambient light was turned off. Graph 12 of FIG. 1B was derived from signals received from another barcode scanning process when the ambient light was turned on. Specifically, the barcode scan signals were obtained using a Honeywell model 1200g laser scanner and the ambient light was a Philips LED desk lamp model 69195. As can be seen from the barcode scan signals obtained in the signal analysis test, the presence of the LED lamp in the vicinity of the barcode reader creates such noise that a barcode cannot be decoded.
Therefore, a need exists for laser-based barcode scanners or barcode readers to operate properly in the vicinity of high-frequency flicker illumination of certain types of ambient light sources.